Friction device for damping shimmy in caster wheels



sept- 27', 1949- A. E. BISHOP 2,482,961

FRICTION DEVICE FOR DAMPING SHIMMY IN CASTER WHEELS Filed Jan. 16, 1948 F/Qi. 6

Patented Sept. 27, 1949 FRICTION DEVICE FOR DAMPING SHIMMY A mcAsTERWI eELs' Arthur E. isho C at woq l n r Sl -liner! fievflt k Austra a" Application January 16, 1948, Serial No. 2,763

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frictional type qr ul r s tant? ee es ala- 5e and e her ebleets at he n enti n an he fi l-1 2$ i ei at et ils at he nstrue: ime eeeratiee we? aexeinaiter .fully r1 Qlai ns. (01, 1

an airplane. swivel *3 1 plan i e! 9?. t e frictio al. esistanc at? from the u id t nt .h qw r Q Beds i the; ln e r e remvs and; p9 tlpniand E a iew t Eiesh w n th el t v fies iiqe 9f n. n sts when turn d t a llrlii e nps t ea-f h reterence to dr wing t e esen in- 21 19.1 s. il us rat d; cQniuactiQn with e S s w el l-llq ai crai-tas lmwnin E g- 1,

rptatiqaal y mounted in asa oumalbearns Q3} sa d oc and s fused to. an ai cr either i dly q retra tably well-known manner.

A. iricliqnal tp slue resis ance devi de crd n tq the, resent nrent en compri es at eas a e pla e I 5 has/inga generally annu a poriqn. l and nou wardly projecting generally t n ula pnr ion ll. of approximately the sam Width a the ameter of the annular plate. poron 15- The plate I5, is. provided with a radial slot 18 therein which at its outer end intersects centrally a crosswise or transverse slot [9' in the plate portion I1 thus ior-ming'a Fr-shaped opening in the plate l5. At the diametrically opposite side of the plate 15 from the radial slot 18 therein,

7 there is an inwardly, directed radial projection 20 having a head portion]! of substantially circular configuration which has its center 22' disposed radially outward from the center 23 or the plate portion 16 (in its iii-line positi'0n,'Eig. 35 a distance about qfne-qu arter the radial dinrension of said plate portion'lli. Secnred int he annular plate portion I 6 circi n eeaa yt :14. ome posed 9i 1h ving a h h cgeflicient of frice d elee i d t ns 6 .s 9 thebla e I Arranged at opposite sigigs eeele t wa t ei c n lQW e plates 3 and 3?! r pe ti which, ar onn cte to e her and e ured a ainst rotation relative to, each 9th?! b means 01 studs 9 whi pass hrough the upper over plate 2 wardly f the plate annu ar por ion 16 and have t ei lowe ends, threaded into the lower cover a1 am in d i e plate 28, for example, as shown in Fig. 2 of the drawing.

The upper cover plate 21 is provided with an upwardly extending concentric hub or neck portion 33 in which is rotatably journaled a spindle 3|, for example, by means of a bearing 32. The upper end of the spindle 3| is fixedly secured, for example, by a pin 34, in the outer extremity of a boss or projection 35 which is provided on the strut casing l3 and extends rearwardly therefrom in a direction corresponding to the in-line position of the caster wheel so that the axis of the adjacent spindle 3| lies in a vertical plane containing the in-line axis of the assembly. The plate 21 is provided with a concentric recess 21a and the spindle 3| is provided with an enlarged flat base portion 36 which is recessed in said recess 21a and disposed intermediate the cover plates 21 and 28. The base portion 36 is provided with a cut-out or recess 31' corresponding substantially to the circular head portion 2| of the plate l5. The circular head portion 2| is received in the cut-out 31 and provides for limited rotation of the plate l in the horizontal plane relative to the spindle 3|.

Secured in overlying relation upon the upper cover plate 21 by means of the aforesaid studs 29 is an actuator plate 39 which is bored to clear the cover plate hub portion 39 and is provided in its normally forward portion with an elongated radially extending slot 40 that is open at its outer end. Normally engaged within the elongated radial slot 49 in the plate 39 is a depending pin 4| which is carried at the outer end of a rearwardly projecting lug portion 42 provided on a collar 43 that is secured to the fork H for rotation therewith relative to the wheel stock casing |3. The plate 39 is maintained seated upon the upper cover plate 21, and the latter and the lower cover plate 28 are urged into gripping or clamping engagement with the friction pads 26 at opposite sides of the plate l5, by means of coil springs or the like 45 which surround the aforesaid studs 29 and act between the upper surface of the actuator plate 39 and the underside of nuts or the like 46 threaded on the upper ends of said studs, for example, as shown in Fig. 2 of the drawing.

Relative rotation of the plate [5 with respect to the spindle 3|, which is fixedly mounted, is opposed by springs 48 of suitable strength arranged in the slot l9 at-respectively opposite sides of an arm or lever 49 that is secured in a recess 5|] provided in the underside of the spindle base portion 35. The arm 49 extends radially of the spindle 3| outwardly through the slot IS in the plate l5, and the springs 48 are retained in the slot l8 relative to the arm 49 by means of dowels or the like 5| which extend within the spring coils and have their inner and outer ends slotted to receive the outer end portion of the arm 49 and the plate portion l1, respectively, as shown.

In operation of the device, as the wheel |0 casters in one direction from the in-line position, carrying with it the fork II and collar 43, the pin 4| carried by the latter and engaged within the slot 49 causes the plate 39 to rotate in the opposite direction carrying with it the upper and lower cover plates 21 and 28. The intermediate plate |5 tends to rotate with the cover plates 21 and 28 by reason of its frictional engagement therewith but is restrained by reason of the fact that the center 22, about which the plate |5 rotates, is offset from the rotational center of the spindle 3| about which the plates 21 and 28 rotate. This causes a restraining torque to be ex- A erted which is the product of the shearing forces of the surfaces in frictional contact and the lateral displacement of the two axes of rotation 22 and 23, respectively.

The restraining torque at the commencement of movement in the illustrated embodiment of the inventionnormally will be about one-fourth the amount of torque exerted by the surfaces in frictional contact when full rotation occurs and, as further relative rotation takes place between the cover plates 21 and 28 and the intermediate plate l5, the arm 49 compresses the spring 48 which is opposing movement of the plate l5 until a condition of equilibrium is reached, for example as shown in Fig. 4 of the drawing, at which time the relative shearing movement ceases and rotation occurs in opposition to uniform restraint, With reference to Fig. 4, the device is illustrated with its several parts in the relative positions occupied thereby when the actuator plate 39 has been rotated about the center 23 through an acute angle a and the intermediate plate |5 has been actuated about the center 22 in the same direction throughan acute angle b by frictional engagement of said plate |5 with the upper and. lower plates 21 and 28. In rotating through the acute angle 1), the center 23 of the plate I5 has moved laterally the distance between the center 23 and a point 52, and substantially all of this lateral displacement of the center 23 takes place in the first few degrees of rotation of the actuator plate 39 with the result that the torque resistance of the device and the commencement of movement of the intermediate plate is the product of the total force required to drag the intermediate plate l5 laterally between the cover plates 21 and 28, and the distance betweenthe centers 22 and 23. In the normal operation of the device, for

example during taxi and turning operations of an aircraft, small oscillations of the swivel wheel are transmitted to the intermediate friction plate l5 with consequent slight shearing movement of the surfaces in frictional contact. This allows the wheel l9 readily to respond to castering forces while an initial and sudden great deflection of the wheel will be effectively clamped by the immediate operation of the device.

From the foregoing it will be observed that the present invention provides a novel torque resistance device of the frictional type which is operable for damping swivelling oscillations or shimmy in caster wheels without limitation of normal turning movement of the caster wheel stockpivot. The invention further provides a novel frictional resistance device having the features and characteristics set forth which is of relatively simplified construction, is comparatively inexpensive to manufacture and maintain, and is highly eificient and effective in operation and use.

'While a particular embodiment of the invention is illustrated and described herein, it is not intended that the invention be limited to such disclosure and changes and modifications may be made therein and thereto within the scope of the claims. I

I claim: 5

1. In apparatus for damping oscillations of a swivel caster wheel element rotatably mounted in a relatively fixed bearing element comprising an actuator member pivotally associated with one of said elements and having a radial slot formed therein and a pin secured to the other of said elements and normally operable in said slot to turn said member upon relative rotation between KMQM.

said: e ements; means; ion retarding free: pivotal mavementzoizsaida actuator.- member th ou hout predetermined an l .,oiroperatineranae there of fiz damp; oscillations of: sai whee1..e ment wit -in a nn determined: an le ffCQ ro1-1e i rota: tion includinaathlete rotatab e; with. said actual: tonm mhen. aifrietion mem n rotatable re at ve plate anddn:frictiona rcontact therewith ten ing; to cause. said iction-1 em er to rotate hz-thesplate, and; sprin meansz pnos n rota: ionimovement or-theiriction. memher i either imQ i fi-i and} tendin normally to center; the; same-,1 1 j:

ap aratus; for? damping; oscillations ofr a sw vel caster Wllfifil? lement rotatably: mounted n; a re atin lsr-fi ed bearing element comprising n actuator memb r; pivotally ssociated; with one o s id: elem nts nd havin a radial slot; formed: therein and; a; pin secured to the: other of: said: el m nts an ino mally pe able in said: slot; a turn; said: member upon relativee t etw en said e ements, r retarding fre pivotal movement of said actuator member throu hout a; predetermined angle of oper tin range thereof to damp oscillations of said wheel element n. a predeterm ned, angle of controlled rotation including a plate rotatable with said actuator member, a friction member adjacent said plate and rotatable relative thereto, elements of high friction coefficient carried by said friction member in frictional contact with said plate tending to cause the friction member to rotate therewith, and spring means opposing rotational movement of the friction member in either direction and tending normally to center the same.

3. In apparatus for damping oscillations of a swivel caster wheel element rotatably mounted in a relatively fixed bearing element comprising an actuator member pivotally associated with one of said elements and having a radial slot formed therein and a pin secured to the other of said elements and normally operable in said slot to turn said member upon relative rotation between said elements, means for retarding free pivotal movement of said actuator member throughout a predetermined angle of operating range thereof to damp oscillations of said Wheel element within a predetermined angle of controlled rotation thereof including a plate rotatable with said actuator member, a friction member rotatable relative to said plate about a center offset from the center of rotation of said plate and in frictional contact with the plate tending to cause said friction member to rotate with the plate, and spring means opposing rotational movement of the member in either direction and tending normally to center the same.

4. In apparatus for damping oscillations of a swivel caster wheel element rotatably mounted in a relatively fixed bearing element comprising an actuator member pivotally associated with one of said elements and having a radial slot formed therein and a pin secured to the other of said elements and normally operable in said slot to turn said member upon relative rotation between said elements, means for retarding free pivotal movement of said actuator member throughout a predetermined angle of operating range thereof to damp oscillations of said wheel element within a predetermined angle of controlled rotation thereof including a plate rotatable with said actuator member, a friction member rotatable relative to said plate about a center oifset from the center of rotation of said plate, elements of h h riotiom coefiicient:-.. carried: by. said member and; i frictional-r contact with said; plate tendin ta, causelsaida fric ion; membe s tolrollatet with, the plate; an pr n means; oppo ing, rotationalmovemcnt: of-themember-in eithen direction and tending normally to center the, same.

5:. In apparatus fon damping. oscillations of swivelcaster wheel' element rotatably mounted in, a relatiyvelafixedbearing element; comprising an, actuatormember pivotallyv associated with. one of said elements and having,- a. radial; slotformed: therein. and a. pin securedto, the, other of: said, elements. and. normally operable in: said: slot to: turn: said: member upon relative, rotation between said elements, means r for retarding, free pivotali movement: of said actuator member, throughoutra predetermined angle of operating range. thereofe to damp oscillations of said; wheelelem-ent withina, predetermined angle of con: trolled: rotation thereo-t including I a pair: of re1a tivelyespacedplatesirotatable with. said actuator member, a friction, member intermediate, said plates rotatable relative thereto, and; in, frictional contact therewith tending to causesaidfrictign member" to rotate. with, the, plates, and: spring m n ppo ingrotational: movement of the member in either direction and tending normally to center the same.

6. In apparatus for damping oscillations of a swivel caster wheel element rotatably mounted in a relatively fixed bearing element comprising an actuator member pivotally associated with one of said elements and having a radial slot formed therein and a pin secured to the other of said elements and normally operable in said slot to turn said member upon relative rotation between said elements, means for retarding free pivotal movement of said actuator member throughout a predetermined angle of operating range thereof to damp oscillations of said wheelelementwithin a predetermined angle of controlled rotation thereof including a pair of relatively spaced plates rotatable with said actuator member, a friction member intermediate said plates rotatable relative thereto about a center offset from the center of rotation of said plates and in frictional contact with said plates tending to cause said friction member to rotate with the plates, and spring means opposing rotational movement of the member in either direction and tending normally to center the same.

7. In apparatus for damping oscillations of a swivel caster wheel element rotatably mounted in a relatively fixed bearing element comprising an actuator member pivotally associated with one of said elements and having a radial slot formed therein and a pin secured to the other of said elements and normally operable in said slot to turn said member upon relative rotation between said elements, means for retarding free pivotal movement of said actuator member throughout a predetermined angle of operating range thereof to damp oscillations of said wheel element Within a predetermined angle of controlled rotation thereof including a pair of relatively spaced plates rotatable with said actuator member, a member intermediate said plates and rotatable relative thereto about a center offset from the center of rotation of said plates, elements of high friction coefiicient carried by said member and in frictional contact with said plates tending to cause said member to rotate with the plates, and spring means opposing rotational movement of the member in either direction and tending normally to center the same. 7

8. Apparatus for damping oscillations of a swivel wheel comprising a rotatable plate, a, friction member rotatable relative to said plate and in frictional contact therewith tending to cause said friction member to rotate with the plate, means actuable by the swivel wheel to rotate said plate in response to oscillations of said wheel, and means opposing rotational movement of the friction member in either direction tending normally to center the same and restraining rotation of said plate.

9. Apparatus for damping. oscillations of a swivel wheel comprising a rotatable plate, a friction member adjacent said plate and rotatable relative thereto, elements of high friction coefilcient carried by said friction member in frictional contact with said plate tending to cause said friction member to rotate with the plate, means actuable by the swivel Wheel to rotate said plate in response to oscillations of said wheel, and means opposing rotational movement of the friction member in either direction tending normally to center the same and restraining rotation of said plate.

10. Apparatus for damping oscillations of a swivel wheel comprising a rotatable plate, a friction member rotatable relative to said plate about a center ofi'set radially from the center of rotation of said plate and in frictional contact therewith tending to cause said friction member to rotate with the plate, means actuable by the swivel wheel to rotate said plate in response to oscillations of said wheel, and means opposing rotational movement of the friction member in either direction tending normally to center the same and restraining rotation of said plate.

11. Apparatus for damping oscillations of a swivel wheel comprising a pair of relatively spaced plates rotatable as a unit in response to oscillations of the swivel wheel, a member intermediate said plates rotatable relative thereto about a center offset from the center of rotation of said plates, elements of high friction coefficient carried by said member and in frictional contact with said plates tending to cause said member to rotate with the plates, and means opposing rotational movement of said member tending normally to center the same and restraining rotation of the plates.

ARTHUR E. BISHOP.

No references cited. 

